The present invention relates to the manufacture of a coil on a toroidal magnetic circuit provided with an air gap.
Many electric apparatuses comprise a coil surrounding a toroidal magnetic circuit having an air gap. They are in particular zero-flux Hall-effect current sensors, self-inductors, transformers with an air gap.
To produce these coils, there is employed a shuttle or spool previously loaded with conductor wire which is passed around the magnetic circuit so as to lay, upon each revolution, a turn of wire on the magnetic circuit.
This method has several drawbacks. In particular, the conductor wire undergoes considerable tensions which requires the use of a conductor wire provided with a relatively thick insulating coating so that, for a given number of turns, there is an increase in the overall size of the coil which results in a limitation in the maximum possible number of turns for a magnetic circuit of given size. Further, with this known method, the precise control of the number of turns, of the distribution of the turns and of the length of wire employed is difficult, which limits the precision obtainable for the electrical characteristics of the apparatus thus obtained. In particular, with this method, it is impossible to produce a coil having a constant outside diameter. It is necessary to produce more turns in the central part than at the ends of the coil. Consequently, for a given number of turns, the maximum diameter of the coil is much larger than the outside diameter of an equivalent cylindrical coil. Lastly, this method is relatively costly.